im not sure but i could have swore that the 24mhz thingy came as an option on my TV not my PS3, could be wrong but i never noticed it till i got my new TV.
i have a 52" Sony BRAVIA XBR 1080p LCD with 120Hz
and ya i can tell a big differnce when 24mhz is enable, not sure if its cause of my TV but WOW! man thats all i can say about it.